Ofertas trabajo programador freelanceJobb

...adecuado para su trabajo mediante la negociación a través de un chat en tiempo real. Video demostrativo: Porfavor mira este video de 2 minutos para entender este proyecto, se solicita uno similar ? FUNCIONES DEL SISTEMA: de Estudiante: Registro y Perfil: Los estudiantes podrán crear una cuenta con sus datos personales y académicos, incluyendo su institución, carrera y nivel de estudios. Publicación de Tareas: Los estudiantes podrán publicar sus tareas o exámenes, especificando el tema, la fecha límite, la complejidad, la recompensa que están dispuestos a pagar y adjuntando los archivos necesarios. Evaluación de Ofertas: Los estudiantes podrán revisar las ofertas de los tutores...

...Your task will be to craft highly engaging and insightful educational articles for a weekly newsletter I'm launching. Key Points: - **Target Audience**: My newsletter is exclusively aimed at freelancers. The content should be tailored to their needs, challenges, and aspirations in the freelancing world. - **Content Type**: I'm looking for educational articles. These could cover topics like freelance productivity, time management, client relationship building, skill enhancement, and so forth. - **Frequency**: You'll be required to produce this content on a weekly basis. Ideally, you should have: - **Proven Experience**: To be considered, you should have a strong portfolio of writing within the freelancing or related industry, particularly in producing educationa...

busco un locutor que tenga la voz estable y entendible, con un microfono bueno. No busco una voz profesional pero si alguien que tenga una voz para enganchar a la gente que mira los videos, que entregue la voz fluida y ya editado el audio. es un trabajo seguro a largo tiempo.

...eye for design who can make the newsletter visually appealing and professional. - Audience Focused: The content of the newsletter should be tailored and engaging for experienced freelancers, providing them with valuable insights and tips that can help them excel in their freelance careers. Ideal Skills and Experience: - Proven experience in designing newsletters, specifically for experienced professionals. - Familiarity with email marketing tools for managing and sending out newsletters. - Strong understanding of the freelance industry and the needs of experienced freelancers. This is a long-term project, so I'm looking for a freelancer who can commit to a weekly update schedule and deliver consistently high-quality work. Your goal is to help build a loyal readershi...

Se buscan trabajadores Requisitos: Ser mayor de edad y nacido en España. Fecha y pago: Domingo 19 de Mayo online (reunión de zoom) 15-30 mins. 8 euros. Descripción del trabajo: Moderaré un grupo de integrantes en un reunion de zoom (no hace falta camara solo audio) y enseñaré un texto en castellano traducido del inglés, lo leeré en alto y los participantes me diran si suena a castellano natural o si hay algun fallo linguístico. Por lo general los textos estan correctamente corregidos excepto algún que otro término. Son cuestionarios médicos de medicamentos y para ser usados en España necesitan la validación de nativos ser entendibles para ser usados en el país.

preciso um programador para terinar meu site

Hallo Facebook marketing freelance

Estoy buscando un programador para hacer un software en windows (igual es mejor opcion hacerlo version web) para apuestas personalizado. Seria un comparador de cuotas entre varias casas de apuestas ,betburger o oddstorm con la diferencia que aqui buscaria las mejores cuotas para hacer lo que se conoce apuestas seguras o surebets. Pongo un ejemplo. se enfent jack sinnerl vs Novak Djokovic. En una casa de apuestas esta rafa nadal a cuota 4 y en otra sale Djokovic a cutoa 1,50. Seria una surebet, ya que pase lo que pase habria beneficio. Para ello se necesita un software que escanee las diferentes cuotas de las casas de apuestas hasta encontrar 2 cuotas donde siemrpe haya beneficio. Es complejo de explicar por escrito. Un saludo

Queria um programador para desenvolver um servidor ou se já tiver um pronto atualizá-lo. Negociaremos os valores.

Se buscan trabajadores Requisitos: Ser mayor de edad y nacido en España. Fecha y pago: Domingo 19 de Mayo online (reunión de zoom) 15-30 mins. 8 euros. Descripción del trabajo: Moderaré un grupo de integrantes en un reunion de zoom (no hace falta camara solo audio) y enseñaré un texto en castellano traducido del inglés, lo leeré en alto y los participantes me diran si suena a castellano natural o si hay algun fallo linguístico. Por lo general los textos estan correctamente corregidos excepto algún que otro término. Son cuestionarios médicos de medicamentos y para ser usados en España necesitan la validación de nativos ser entendibles para ser usados en el país.

Description: We are currently seeking a dynamic and motivated freelance cold caller to join our team and assist in prequalifying low-income prospects for our revolutionary no-cost health benefits program. This is an excellent opportunity for individuals who are skilled in high-volume cold calling and have a passion for helping others access essential healthcare services. Responsibilities: -Make outbound cold calls to potential prospects to prequalify them for our no-cost health benefits program. -Conduct approximately 100-200 calls per day with a focus on efficiency and effectiveness. -Engage prospects in a professional and empathetic manner to gather necessary information. -Use qualifying questions to determine eligibility based on income level and current health coverage. -Clea...

Logo Name : SCENELABS We're SCENELABS, a company passionate about helping photographers create stunning scenes! We provide high-quality photography props like platters, slate rocks, sand, and a variety of other creative elements. To elevate our brand identity, we're seeking a talented freelance designer to craft a logo that captures the essence of SCENELABS. Here's what we envision: Simple yet eye-catching typography: The name "SCENELABS" should be clear and memorable, using a font that is both modern and professional. Incorporation of photography props: We'd love to see a hint of our products in the logo design. This could be a simple shape like a plate, a rough texture like rock, or a few dots like sand. Overall brand message: The logo should evok...

Necesito alguien para pasar a latex paginas de ejercicios escritas a mano, necesito que el que las pase sepa de estadistica, me de feedbacks para revisar que las escribe bien, sea dedicado y haga un buen trabajo, pago por pagina 50 centimos.

Marcia te envío lo que fue de abrily separo la propuesta nueva si te parece. lo que hicimos en abril es lo mismo que veniamos trabajando en campañas de mubit usd$300 sumamos a partir de mayo dos campañas más, pinterest y comenzaremos a hacer campañas de e mail marketing. Me gustaría que podamos ir armando poco a poco toda la est...de mubit usd$300 sumamos a partir de mayo dos campañas más, pinterest y comenzaremos a hacer campañas de e mail marketing. Me gustaría que podamos ir armando poco a poco toda la estructura para que tengas el equipo de marketing ocmpleto asi que me pondré a buscar un diseñador que haga la estética para redes así tengo yo anuncios nuevos de calidad. En...

I'm looking for a dynamic sales executive to help generate leads for my technology business. - Industry: Technology - Primary Goal: Lead Generation - Target Audience: Mid-sized companies The ideal candidate will possess: - Proven experience in lead generation, preferably within the technology industry - Excellent communication and negotiation skills - A strong understanding of the sales process - A good network of contacts within mid-sized companies (Business Development Executive) (with good track record) + Must have strong Sales Managerial Experience in any B2B SaaS company OR been as a Sales Partner. + Experience in dealing with B2B + USA / EU Markets + Must be interested in taking on new challenges. + Should have hands-on experience. + Only Freelancers are Allowed (No Agenc...

Hiring Freelance Sales Expert: Guaranteed 100+ Monthly Sales Are you a dynamic sales expert with a proven track record of driving significant results? We are looking for a talented individual to join our team at KHLuxuryShopping as a Freelance Sales Expert. About Us: KHLuxuryShopping is an exclusive online destination offering luxury products curated from around the world. From fashion to home decor, our platform caters to discerning customers seeking unique, high-end items. Job Description: As a Freelance Sales Expert, your primary goal will be to generate a minimum of 100 sales per month for KHLuxuryShopping. You will leverage your sales expertise and network to drive customer engagement and increase conversions on our platform. Responsibilities: Develop and exe...

...subtitular un video MP4 al español, con el uso de Aegisub o Workshop. El video tiene una duración de 35 a 40 minutos y el trabajo final debe entregarse en formato .srt. - Traducción: Necesito una traducción fiel y precisa del árabe al español de España, garantizando una máxima fidelidad en el contenido y contexto del video. - Experiencia en Subtitulado: Se requiere experiencia previa en subtitulado para asegurar la correcta sincronización de los subtítulos con el video, manteniendo un ritmo apropiado y coherente. - Herramientas: Es imprescindible el manejo de software de subtitulado como Aegisub o Workshop para llevar a cabo este proyecto con eficiencia y calidad. el trabajo tendria que estar en 3 dia...

Necesito un desarrollador web profesional y creativo para diseñar un sitio web de portafolio. El propósito de este sitio web es mostrar mi trabajo en la creación de contenido para redes sociales y campañas publicitarias. Requisitos clave: - Diseñar un sitio web visualmente atractivo y fácil de navegar que muestre efectivamente mi contenido. - Integrar un formulario de contacto para que los posibles clientes o empleadores puedan comunicarse conmigo. - Incluir una sección de blog que pueda usar para discutir mi trabajo, las tendencias de la industria y compartir ideas. Habilidades y experiencia: Competencia en diseño y desarrollo web. Experiencia en la creación de portafolios o sitios web personales. Fuerte comp...

Bonjour,Je développe actuellement un SaaS de gestion RH pour entreprises et agences de recrutement en PHP. Je cherche un designer freelance pour prendre en charge le design de l'interface utilisateur et de la landing page une fois le projet fonctionnel terminé.Tâches à réaliser :Design de l'interface utilisateurCréation de la landing pageModification des fichiers de style et de la structure HTML tout en conservant la logique intacteCompétences requises :Expérience en design UI/UX pour applications SaaSMaîtrise de HTML/CSSCapacité à travailler sur un projet existantDélai : 3 mois Si vous êtes intéressé, merci de me contacter avec votre portfolio et vos , Megret Micha

I'm looking for a full-stack developer to create an online job platform where job seekers can find and apply for full-time and freelance job opportunities. I need this project to be completed as soon as possible. Key Features: - Full-time and Freelance Jobs: The platform should support posting, searching, and application of full-time and freelance job opportunities. - User-friendly Interface: Intuitive design enabling easy navigation and job application. - Job Alerts: Implement a feature that allows job seekers to get notified whenever a new job matching their criteria is posted. Ideal Candidate: - Proven experience in full-stack development, particularly in building similar platforms. - Strong understanding of user experience design and development. - Ability ...

I am on the lookout for an adept freelance copywriter who is proficient in both German and English. Our need primarily concerns: - Crafting content for brochures and website edits - Ideally, the copy will maintain a balanced approach, merging technical specificity with more general appeal to convey our B2B software-as-a-service (SaaS) offerings to potential customers. Your ability to deliver clear, persuasive, and engaging writing optimized for a B2B audience is critical for this project. In addition, you may occasionally be tasked with creating social posts, reports, blog posts and providing translations from English to German, making bilingual proficiency a must. Our German marketing team largely focuses on our SaaS product (specifically, our learning management system, Spark...

READ CAREFULLY - THIS COULD BE A LUCRATIVE OPPORTUNITY FOR THE RIGHT PERSON OR AGENCY We're looking for a talented and passionate AI enthusiast / specialist to work along site us catering to our clients About Us: We are a leading AI solutions agency based in London, UK, specializing in AI services tailored for small to medium-sized businesses (SMBs) across the UK and Europe. We are currently seeking a highly motivated individual or agency to collaborate with us in setting up these systems for our current clients. About You: Technical Skills: - Experience with cloud-based AI platforms (e.g., Dialogflow, Rasa, Bland AI, Open AI, Pipedream, Make, Zapier etc) - Strong understanding of natural language processing (NLP) concepts - Familiarity with API integrations - Experience with p...

Necesito urgentemente una persona talentosa que pueda ayudarme a editar resúmenes de episodios de animes en español. Habilidades y experiencia ideales: - Dominio de español - evitar el copy - Experiencia previa en la creación o edición de resúmenes de episodios. - hacer el trabajo rapido - tener buen internet - trabajo a futuro

...the Department of Biotechnology, Government of India and are award holders for the ‘Best Innovation in the healthcare sector 2014’ courtesy BIRAC. They are an ISO 9001:2015 certified company. Be a part of Morning Fresh’s fast-growing team and become an integral part of their journey as they launch more exiting wellness beverages! Job Title: Freelance Video Creator and Editor Location: Remote Morning Fresh is seeking a talented and creative Freelance Video Creator and Editor to join our team. In this role, you will collaborate with our team to produce engaging video content that reflects our brand identity and resonates with our target audience. You will be responsible for conceptualizing, filming, and editing high-quality videos for various marketing c...

salve, per questo progetto mi interesserebbe essere contattato da un freelance x avviare una campagna di lead generation con meta per intercettare in rete delle presentatrici interessate a rivendere i nostri detersivi x la casa con un ottimo rapporto qualita /prezzo ed una soddisfacente provvigione per loro. Tutti i nostri prodotti sono esposti sul sito zona di ricerca napoli e provincia perche lavoriamo con consegna gratuita

I'm in need of a freelance electronics engineer with experience in LTSpice to design a voltage converter for me. - Purpose: The desired converter is a voltage cuck converter, meaning it should be able to change the voltage of the input signal. - Output Characteristics: The voltage output should be adjustable, allowing for flexibility in use. The output voltage range is 240 - 346 volts. - Maximum output current is 87 A. - Maximum rate of change of inductor current is 34.5 - Maximum Power is 30 kW. - Input Voltage Range: The input voltage range should be 330 to 550 volts. - Switching frequency is 150 kHz. - The project is only a simulation in LTspice. The ideal freelancer for this job should have: - Experience in LTSpice and a proven track record of designing voltage conver...

I'm in need of a freelance electronics engineer with experience in LTSpice to design a voltage converter for me. The budget of the project can be much higher than 30$. - Purpose: The desired converter is a voltage cuck converter, meaning it should be able to change the voltage of the input signal. - Output Characteristics: The voltage output should be adjustable, allowing for flexibility in use. The output voltage range is 240 - 346 volts. - Maximum output current is 87 A. - Maximum rate of change of inductor current is 34.5 - Maximum Power is 30 kW. - Input Voltage Range: The input voltage range should be 330 to 550 volts. - Switching frequency is 150 kHz. - The project is only a simulation in LTspice. The ideal freelancer for this job should have: - Experience in LTSpi...

I'm seeking a talented freelance graphic designer to help create a dynamic logo that primarily focuses on a slogan or tagline. There are no pre-determined color preferences - I want you to feel free to explore the color spectrum and choose the most visually appealing color scheme that reflects our identity. The logo must effectively and clearly communicate innovativeness and creativity, emphasizing an up-to-date and trend-setting approach. Ideal Skills and Experience: * Proven experience in graphic design * Portfolio of completed logo designs * Knowledge of current design trends * Proficiency in Adobe Illustrator and Photoshop * Creativity and out-of-the-box thought process is a must-have Your role will be the driving force in creating a logo that leaves an impact and ma...

I'm in need of a robust website that is both visually appealing and functional. The website should be designed in a clean and professional style. ...both visually appealing and functional. The website should be designed in a clean and professional style. The most important features I need are: - Customer Reviews: I want customers to be able to leave reviews on services that have been provided - Contact Form: I would like a 'enquire about a quote or information' tab that will send this information to my business email. I'm looking for a freelance web designer and developer who is experienced in creating e-commerce websites and can deliver on both the design and functionality. Your portfolio should reflect a strong grasp of clean, professional design and experi...

Hola. La verdad me encanto tu trabajo, jaja ví que pusiste en tu portafolio, si quedó muy bien Oye quiero unas pequeñas modificaciones, te contacto por chat para quedarbel precio

We are in need of a freelance California certified solar designer to review and certify our solar system design. The project is a 280 kW Rooftop PV System for an estate in Southern California. Our Helioscope model, single line diagrams, layout and cabling schematics are all ready for review. Your expertise will be crucial in ensuring the accuracy and compliance of our design. The ideal candidate will have extensive knowledge and experience in solar system design, as well as the ability to conduct thorough peer reviews. Attention to detail and adherence to local regulations are paramount.

Hola, Tengo un wordpress 6.5 con elementor 3.20 y tengo un problema con el proceso de paginado. He encontrado información sobre el posible problema pero no logro que me funcione correctamente. https://davidloor...com/2024/01/06/fix-duplicate-content-elementor-loop-grid-widget-pagination/ Necesito que el interesado tenga los siguientes Skills: - Experiencia en WordPress con versión 6.5. - Experiencia con Elementor. - Experiencia en resolución de incidencias. - Experiencia en modificación de código PHP sobre capa Wordpress. - Conocimientos con la capa de plugins de Wordpress. Para esta oferta, únicamente se aceptan ofertas para usuarios de habla hispana. En cuanto al acceso a la plataforma para analizar el problema, se realizará d...

Hi Everyone Since you are on DevOps, Freelance at MFH Please find projects here and apply : Competitive rates. ----------------------------- Regards, MFH IT Solutions (GST ID: 37ABWFM7509H1ZL) ☎️ Contact Us MFH LinkedIn

I'm seeking a freelancer with data entry and copywriting skills to work on a project that generates income through freelance writing. Key Tasks: - Data Entry: involves inputting, updating, or verifying data in a system or database. - Copywriting: creating persuasive and engaging written content to promote or sell a product, service, or idea. The ideal candidate should have: - Proven experience in data entry and copywriting - Strong attention to detail and accuracy for data entry tasks - Excellent writing and editing skills, with a focus on copywriting - Understanding of SEO principles for copywriting is a plus This project is perfect for someone with a passion for writing and the ability to generate income through their work.

...comparar precios de productos en farmacias. La aplicación inicialmente se enfocará en Pamplona y sus alrededores, pero está diseñada para expandirse a toda la península en el futuro. Las características principales de la aplicación incluyen: 1. **Comparación de Precios**: Los usuarios podrán buscar productos y comparar los precios en diferentes farmacias cercanas. 2. **Ofertas y Descuentos**: La aplicación mostrará ofertas y descuentos disponibles en las farmacias. 3. **Descuentos por Compra en la App**: Se ofrecerán descuentos adicionales a los usuarios que realicen compras a través de la aplicación. 4. **Integración con Google Maps**: La aplicación estar&...

I'm looking for an accountant(Freelance / Intern / Permanent Employment) who is well-versed in Zoho Books and Zoho Payroll to set up and manage the financial aspects of my startup. Key Responsibilities: - Initial setup of Zoho Books & Payroll software - Bank account reconciliation - Bookkeeping - Managing payroll and salaries Additional Details: - Preferably no specific requirements for the initial setup. You can set up the software based on the needs of my business. - The tasks will need to be managed on a weekly basis. Ideal Candidate: - Proficient in Zoho Books and Zoho Payroll - Experience in bank account reconciliation, bookkeeping, and payroll management - Strong organizational skills and attention to detail - Good understanding of accounting principles Looki...

I require an experienced freelance audio engineer that can physically join my team for studio recordings. Key tasks involve: - Recording - Mixing - Editing - Mastering - Using Source Connect and Protools The projects are fairly short and simple. Despite this, harmonizing the varied aspects of the task remains important. We primarily mix audio for: - Television - Radio - Social Media Platforms - BVOD The ideal individual should be highly skilled with Pro Tools and Source Connect, and should have experience mixing for the said platforms. It will be beneficial if you've had experience in the media industry. Your abilities to work on varied platforms further strengthens your application. You will be paid on an hourly rate.

I am looking for a photographer and videographer Location: Pondicherry is more comfortable Looking for long term and also willing to travel all over tamil nadu ( need required ) Language: tamil ( must ) & English As a business owner in need of high-quality product photographs, I'm currently looking for a freelance photographer with an exceptional eye for detail and creativity. Key Requirements: - Proficiency in product photography: You should have experience in capturing products in a way that highlights their features, and makes them visually appealing. - Photojournalistic Style: I'm looking for a photographer with an understanding of photojournalism, who can tell a story through their photographs. - High-Quality Results: The final photos should be of a profe...

I'm in need of a skilled freelancer to help me with an ongoing project. I'm currently working on a project, however, I need some extra hands to assist me in its completion. Unfortunately, I don't have a particular expertise in mind, so the position is open to professionals in a wide variety of fields. Responsibilities: - Assist with the development of the project - Provide support on multiple project tasks Ideal skills and expertise may include, but are not limited to: - Programming - Design - Writing The main objective of this collaboration is to enhance the overall quality and timeliness of the project. The successful candidate should be a team player, able to work independently, and possess great attention to detail.

We are looking for an experienced freelancer to create a custom DMA firmware using this simple guide : The guide provides detailed instructions, but I lack the time to complete it myself. The project will be executed on a Squirrel 35t board and should not take more than 3-4 hours for someone proficient. **Tasks:** - Configure and customize firmware based on pcileech-fpga - Use Vivado for development - Emulate TLP and configure the configuration space **Required Skills:** - FPGA design and programming - Experience with Vivado (Xilinx) - DMA firmware development - Verilog/VHDL programming - Debugging and testing embedded systems

...my social media and content creation needs. Your role will include: - Social Media Management: You'll be in charge of my Facebook and Instagram accounts, posting engaging content, responding to messages and comments, and growing our follower base. - Content Creation: I need high-quality content that resonates with middle-aged adults, business people, companies, distributors, resellers, and freelance salespeople. This content should encourage engagement and sharing within these target demographics. - Graphic Creation: You'll also be responsible for creating visuals that accompany our posts. - Paid Ads Experience: I need someone who has experience in managing Facebook and Instagram paid ads, and can use these platforms effectively to reach our target audience. The ...

We are looking for a freelance expert in marketing and market analysis to help us identify high-demand consumer products in the Netherlands that can be successfully sold online. The candidate should be able to analyze market trends and customer needs, and use data and research to identify opportunities and value-added products that can be successfully sold online. Key requirements: - Proficiency in market research and trend analysis in the Netherlands - Experience in identifying and forecasting demand for online selling - An understanding of the competitive landscape in the specified product categories - Strong communication skills and the ability to present findings in a clear and actionable manner The target audience for the products is primarily young adults aged 10-35, so th...

Nos dedicamos hacer funnels a consultores para asi aumentar su facturacion Experiencia : Copy para paginas de venta Estratega digital y creacion de funnels Email marketing

Are you a skilled communicator with a knack for scheduling appointments? Glimmer Grove Design is seeking freelance appointment setters to assist us in reaching potential clients and scheduling Zoom calls to showcase our beautifully crafted websites. Responsibilities: - Utilize provided dialer, script, and lead list to make outbound calls to businesses without websites. - Engage with business owners or decision-makers to discuss our website offerings. - Schedule Zoom calls to present our pre-built website demos. - Maintain accurate records of appointments scheduled. - Requirements: - Excellent communication skills, both verbal and written. - Comfortable making outbound calls and engaging with potential clients. - Ability to effectively follow a provided script while adapting to co...

Estamos buscando un programador Android Studio para crear una app cuyo funcionamiento es conectarse a una base de datos mysql y consultar datos a partir de escanear un codigo de barras o QR. Buscamos a alguien de Argentina o al menos de America Latina.

... y estamos buscando alguien en España para hacer llamadas y captación junto con tareas de organización para nuestro equipo creciente. El trabajo tiene que ver con llamadas a dueños de pisos y casas en venta para conseguir visitas para nuestro fotografo o equipo de ventas. La idea es pagar por hora y también por éxito. Con el tiempo igual buscamos alguien para unirse a nuestro equipo así que vivir en Valencia o cerca sería una ventaja pero no es obligatorio. Inicialmente harzemos una prueba pagado para ver la efectividad y luego contrataremos por meses. Hace falta un nivel alto de inglés pero la mayor parte del trabajo es con llamadas en castellano, organizar Google Sheets y contactar con nuestro equipo por mai...

Se necesita un desarrollador frontend que sepa de ionic con angular para realizar diferentes tareas a lo largo del tiempo. Se requiere un trabajador con el que se pueda contar durante varios meses para trabajar 2-3 horas al día máximo. Debe contar con un Mac para poder compilar la aplicación y publicarla en las tiendas de Apple y Android. La app se llama Racket Score y el trabajo consistiría en mejoras en la app ya existente

Seeking a creative freelance designer to create breathtaking, modern plush toys for toddlers. Ideal skills and experience: • Strong creative design skills and originality. • The ability to incorporate modern aesthetics within the design. • A keen understanding of Canadian design standards preferred. • Legally eligible to work in Canada.

Looking for Freelancer with Skills in Technical and Financial Proposal Writing, Design, and Summary Creation About Us: We are a dynamic event management company specializing in organizing memorable events that celebrate culture, heritage, and unity. Our team is dedicated to delivering exceptional experiences for our clients and their audiences. Opportunity: We are seeking a freelance professional who can assist us in crafting compelling technical and financial proposals for our events. This role involves creating visually appealing designs and themes that align with our clients' objectives and summarizing them into concise proposals that capture attention and secure contracts. Skills Required: Proficiency in writing technical and financial proposals for event management ser...

Necesito programador frontend en Vue3 para corregir estilos css y validaciones frontend