Hello,
Please add this code to the Theme Settings > Custom CSS > Global:
body .mailster-form-1 .mailster-submit-wrapper .submit-button {
padding: 12px 20px;
font-size: 13px;
line-height: 18px;
background-color: #F3F3F3;
color: #3E3E3E;
position: relative;
display: inline-flex;
align-items: center;
justify-content: center;
outline: none;
border-width: 0;
border-style: solid;
border-color: transparent;
border-radius: 0;
box-shadow: none;
vertical-align: middle;
text-align: center;
text-decoration: none;
text-transform: uppercase;
text-shadow: none;
letter-spacing: .3px;
font-weight: 600;
cursor: pointer;
transition: color .25s ease, background-color .25s ease, border-color .25s ease, box-shadow .25s ease, opacity .25s ease;
}
}
body .mailster-form-1 .mailster-email-wrapper input.input {
padding: 0 15px;
max-width: 100%;
width: 100%;
height: 42px;
border-bottom: 2px solid;
border-radius: var(--wd-form-brd-radius);
box-shadow: none;
vertical-align: middle;
font-size: 14px;
transition: border-color .5s ease;
}
Best Regards