These are the global css styles which are mostly used.

/* 
=====================
Variables
=====================
*/

:root{
    --primaryColor:#f15025;
    --mainBlack:#222;
    --mainWhite:#fff;
    --offWhite:#f7f7f7;
    --darkGrey:#afafaf;
    --mainTransition:all 0.3s linear;
    --mainSpacing:0.2rem;
}

/* 
=====================
Global Styles
=====================
*/

*{
    margin:0;
    padding:0;
    box-sizing: border-box;
}

body{
    font-family: 'Fira Code', monospace;
    color:var(--mainBlack);
    background:var(--mainWhite);
    line-height: 1.5;
}

a{
    text-decoration: none;
}
img{
    width:100%;
    display:block;
}

h1,h2,h3{
    text-transform: capitalize;
    letter-spacing: var(--mainSpacing);
    margin-bottom: 1.25rem;
}

h1{
    font-size: 3rem;
}
h2{
    margin-bottom: 0;
}

p{
    font-size: 0.7rem;
    font-weight: 300;
    line-height: 2;
}
/* make anchor tag a  button with class .btn */
.btn{
    display:inline-block;
    padding:0.5rem 1rem;
    text-transform: capitalize;
    border:3px solid var(--primaryColor);
    color:var(--primaryColor);
    margin:3rem;
    transition: var(--mainTransition);
}

.btn:hover{
    background:var(--primaryColor);
    color:var(--mainWhite);
}